Recently, many image sensing apparatuses (e.g., a digital camera and digital video camera) which record an image as data by using an image sensor such as a CCD have hit the market. A digital camera does not require any photographic film which has conventionally been used as a recording medium. Instead, the digital camera records an image as data on a data recording medium such as a semiconductor memory card or hard disk device. Unlike the film, these data recording media enable repetitive write and erase conveniently, and can reduce the cost of consumables.
A digital camera is generally equipped with an LCD monitor device capable of displaying a photographed image on request, and a removable large-capacity storage device.
By using the digital camera having these two devices, a film serving as a recording medium which has conventionally been used as a consumable need not be used, and a photographed image can be displayed and confirmed on the LCD monitor device at once. The user can erase unsatisfactory image data on the moment, or if necessary, photograph an object again on site. Compared to a photograph using a photographic film, the photographing efficiency significantly rises.
With this convenience and technical innovation for a larger number of pixels of an image sensor, the utilization of digital cameras is becoming wider. These days, lens exchangeable type digital cameras such as a single-lens reflex digital camera are also available.
Unlike a film camera in which the film is transported every photographing, a digital camera takes a picture by always using the same image sensor. Dust and mote (to be generally referred to as “dust” hereinafter), which attach on an image sensor, an image sensor protective glass fixed to the image sensor, the surface of an optical filter or the like, and an optical system (to be referred to as optical system components of the image sensor at once hereinafter), stay there unless they are removed. At the position at which dust attaches, dust shields light to inhibit photographing, degrading the quality of a photographed image.
In not only a digital camera but also a camera using a photographic film, if dust exists on a film, it is also photographed. However, the film is transported every frame, and the same dust is hardly sensed successive frames.
To the contrary, the image sensor of the digital camera is fixed and not transported, and a common image sensor is used for photographing. Once dust attaches to the optical system component of the image sensor, the same dust is sensed in many frames (photographed images). Especially in a lens exchangeable type digital camera, dust readily attaches in exchanging a lens.
The photographer must always be careful about attachment of dust to the optical system component of the image sensor, and spends much effort on checking and cleaning dust. In particular, since the image sensor is placed relatively deep in the camera, cleaning the sensor and confirmation of dust are not easy. In cleaning, dust may attach adversely.
Dust readily enters the lens exchangeable type digital camera during lens exchange. In addition, most of lens exchangeable type digital cameras have a focal-plane shutter in front of the image sensor, and dust easily attach on the optical system component of the image sensor.
In an image reading apparatus such as a film scanner, a technique to detect dust on a document table or a film document from a read image and correct the image is known (see, e.g., Japanese Patent Laid-Open No. 2003-344953). However, an environment in which the image sensor of an image reading apparatus of this type is placed is greatly different from that of a digital camera. Also, dust detection on a document is focused, and no dust detection on an image sensor is considered.
Since dust readily attaches on the optical system component of the image sensor in the lens exchangeable type digital camera owing to its mechanism, it is important to detect attached dust, how to process detected dust, and photograph an image free from any influence of dust. If dust is left unprocessed, dust is directly sensed into an image. Dust correction at an unnecessary portion owing to a detection error of the dust position or an excessive dust process degrades an image.